package acwing._2LanQiao._3Math_DP;

import java.util.Scanner;

/**
 * @Project : ProgrammingExercises
 * @Package : ACWing._2LanQiao._3Math_DP
 * @File : Q1216.java
 * @Author : WangRuoyu
 * @Date : 2023/3/14 16:17
 */

public class Q1216 {
    public static void main(String[] args) {
        Scanner scan = new Scanner(System.in);
        int n = scan.nextInt();
        int m = 0;
        int res = 0;

        while (n >= 3) {
            res += 3;
            n -= 2;
        }
        res += n;
        System.out.println(res);
    }
}

